Novel polymeric photoinitiators bearing side-chain α-aminoacetophenone moieties for ultraviolet-curable pigmented coatings

New polymeric photoinitiators with pendant α-aminoacetophenone moieties, such as the homopolymers of 1-(4-morpholinophenyl)-2-benzyl-2-[N-methyl-N-(3-methacryloyloxypropyl)]aminopropan-1-one and of 1-(4-morpholinophenyl)-2-benzyl-2-[N-methyl-N-(3-methacryloyloxypropyl)]aminobutan-1-one have been prepared and fully characterized. Their photoinitiation activity has been also checked in the ultraviolet cure of a standard acrylic mixture, under irradiation over 380 nm, thus simulating the absorption conditions of a TiO₂-pigmented coating formulation. The results have been compared with those found by using the corresponding low-molecular-weight structural models, purposely synthesized. The activity data obtained are discussed and related to the structural requirements of the above systems. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2237–2246, 1997     

Copolymeric systems with pendant thioxanthone and α-morpholinoacetophenone moieties as photosensitizing and photoinitiating agents for UV-curable pigmented coatings

The synthesis and structural characterization of copolymers of 1-[(2-acryloyloxy) ethoxycarbonyl]thioxanthone (ATX) with 1-[4-(2-acryloyloxyethylthio)phenyl]-2-methyl-2-morpholino-propan-1-one (AMMP), as well as ATX, AMMP and n-butyl acrylate (BA) terpolymers, is reported. These copolymeric systems have been checked in the photoinitiated polymerization in film matrix of the 1,6-hexanediol diacrylate (HDDA)–BA equimolar mixture under UV irradiation over 380 nm, i.e., under conditions simulating a TiO₂-pigmented acrylic coating formulation, and compared with the corresponding mixture of low-molecular-weight structural models 1-[(2-isobutyroyloxy)ethoxycarbonyl]thioxanthone (ITX) and 1-[4-(2-isobutyroyloxyethylthio)phenyl]-2-methyl-2-morpholino-propan-1-one (IMMP). The much higher photoinitiation activity shown by the copolymers is discussed in terms of close vicinity of thioxanthone and α-morpholinoacetophenone moieties along the backbone, which favors the excitation energy transfer from the former to the latter photosensitive group. © 1995 John Wiley & Sons, Inc.     

Copolymeric photoinitiators containing in‐chain thioxanthone and coinitiator amine for photopolymerization

Two kinds of copolymeric macromolecular photoinitiator, PTXPM and PTXPC, were prepared by introducing methylacryloyl or cinnamoyl groups to the side chain of PTXP. The photopolymerizations of poly(propylene glycol)diacrylate (PPGDA) and trimethylolpropane triacrylate (TMPTA), using PTXPM and PTXPC as photoinitiators, were studied by photo‐DSC. PTXPM and PTXPC have UV–vis spectra similar to that of PTXP with blue‐shift absorption maxima. The photopolymerization behavior of TMPTA, initiated by three photoinitiators, appears similar to that of PPGDA. Compared with PTXP and PTXPC, PTXPM gives higher polymerization rate and final conversion, in photopolymerization of PPGDA and TMPTA, which shows that the introduction of methyl acrylate to the PTXP chain has a greater effect on photopolymerization of PPGDA and TMPTA than that of cinnamoyl acrylate. The polymerization rate and final conversion, for photopolymerization of PPDGA initiated by PTXP, can be more effectively increased by the introduction of methyl acrylate group to the PTXP chain, than are those for TMPTA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2395–2400, 2004     

Polymeric photoinitiators having benzoin methylether moieties connected to the main chain through the benzyl aromatic ring and their activity for ultraviolet-curable coatings

New polymeric UV photoinitiators, bearing the benzoin methyl ether moiety linked to the side chain through the 4′ position, were synthetized by radical homopolymerization of the corresponding monomers, 4′-methacryloyloxy benzoin methyl ether and 4′-methacryloyloxy α-methyl benzoin methyl ether, prepared in turn after a thorough investigation of synthetic methods. For comparison, low molecular weight structural models of the repeating co-units of the polymers having the pivaloyloxy group linked to the 4′ position of the benzoin methyl ether moiety were also prepared. All polymeric and model compounds were fully characterized and employed in the photoinitiated polymerization and crosslinking of a standard acrylic formulation for clear UV curable coatings. The photoinitiating activity of these systems, measured by microwave dielectrometry, indicates a higher cure fastness for the model compounds with respect to the corresponding polymeric derivatives, and such a behaviour is tentatively interpreted in terms of the fragmentation mechanism of the benzyl methyl ether radicals formed on α-photocleavage of the benzoin moiety.     

Polymeric systems bearing side-chain 2,6-dimethylbenzoyldiphenylphosphinoxide moieties for UV curable coatings: Synthesis and photoinitiation activity

Polymeric photoinitiators with pendant 2,6-dimethylbenzoyldiphenylphosphinoxide moieties were prepared by reacting the hompolymer of 4-acryloyloxy-2,6-dimethyl benzoic acid, and its copolymers with n-butyl acrylate with thionyl chloride followed by methoxydiphenylphosphine. These polymeric systems were characterized and their photoinitiation activity checked in the UV curing of a standard acrylic mixture, by irradiation both at 330 and over 380 nm, the latter conditions being applied to simulate a TiO₂-pigmented coating formulation. The results were compared with those obtained by using the low molecular weight analog 2,4,6-trimethylbenzoyldiphenylphosphinoxide and previously prepared polymeric systems based on the benzoyldiphenylphosphinoxide moiety. The stability to light and to hydrolytic conditions of the polymeric photoinitiators with respect to the model compound was also tested. The results obtained are discussed and related to the structural requirements of these systems. © 1995 John Wiley & Sons, Inc.     

Evaluation of new 3‐mercaptopropionate thiols for thiol‐ene photopolymerization coatings using experimental design

Three 3‐mercaptopropionate thiols, 1,6‐Hexane bis(3‐mercaptopropionate) (HD‐SH), trans‐1,4‐Cyclohexanedimethyl bis(3‐mercaptopropionate) (CHDM‐SH), and 4,4′‐Isopropylidenedicyclohexane bis(3‐mercaptopropionate) (HBPA‐SH) were formulated with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione (TATATO) and photoinitiator. The formulations were photopolymerized via thiol‐ene photopolymerization. A ternary experimental design was employed to elucidate the influence the three thiols on the thermomechanical and coatings properties of thiol‐ene photopolymerizable materials. Tensile strength, tensile modulus, elongation‐to‐break, glass transition temperature (T_g), and crosslink density (XLD) were investigated. Coating properties including pencil hardness, pull‐off adhesion, MEK double rubs, and gloss were also investigated. Relative reaction conversion was determined by photo differential scanning calorimeter (PDSC). Thiol‐ene photopolymerizable materials containing HBPA‐SH resulted in improving tensile strength, tensile modulus, T_g, and pencil hardness but lowering of crosslink density and relative conversion. This was attributed to steric and rigidity of the double cycloaliphatic structure. The inclusion of CHDM‐SH into the systems resulted in the synergistic effect on elongation‐to‐break and pull‐off adhesion. The HD‐SH generally resulted in a diminution of thermomechanical and coating properties, but improved the crosslink density. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of oligomers containing the α‐aminoalkylphenone chromophore as oligomeric photoinitiator

An oligomeric photoinitiator containing α‐aminoalkylphenone photoactive chromophore in the main chain was prepared from diphenyl ether, α‐chloroisobutyryl chloride, and piperazine through acylation, bromination, epoxidation, and polycondensation. The obtained oligomeric photoinitiator was characterized by GPC, TGA, traditional DSC, FTIR, NMR, UV–vis absorption, and fluorescence spectroscopy. The number‐average molecular weight (M_n) of the oligomeric photoinitiator was determined to be 2000–4000. The excitation and emission wavelengths of the fluorescence spectra were 376 and 473 nm, respectively. The thermal stability of the oligomer was found to be perfect with a decomposition temperature greater than 300°C. All the spectroscopic and thermal analyses clearly confirmed the consistence of property and structure. In a comparative photo‐DSC investigation, the oligomeric photoinitiator showed high photoinitiating efficiency while using 1,6‐hexanediol diacrylate as monomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3417–3424, 2006     

Coating performance and characteristics for UV-curable aliphatic urethane acrylate coatings containing norrish type I photoinitiators

The purpose of this study was to investigate the influence of several Norrish I (α-cleavage) type photoinitiators and UV dose on the curing behavior and coating performance of UV-curable aliphatic urethane acrylate coatings. UV-curable coatings were cured under a high-pressure mercury lamp. The curing behavior and coating performance of the UV-curable coatings that were cured using 2-hydroxy-2-methyl-1-phenyl-propan-1-one or 1-hydroxy-cyclohexyl-phenyl-ketone were superior to those of the UV-curable coatings cured using bis (2,4,6-trimethylben-zoyl)-phenylphosphine oxide or diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide, when the UV-curable coating was cured in air. Current address: Electronic Chemical Materials R&D Center, CHEIL Industries Inc.     

Tetrafunctional acrylates based on β-hydroxy alkyl amides as crosslinkers for UV curable coatings

Ultraviolet (UV) curable coating formulations were prepared from novel crosslinking acrylates synthesized from β-hydroxy alkyl amides. Variations were done with respect to the nature of the monomer backbone by introducing aliphatic, aromatic and cycloaliphatic structures in between the amide groups. The synthesized multifunctional alcohols and acrylates were subjected to IR and NMR analysis for structure confirmation. The acrylates were dissolved in chloroform and the UV–vis spectrum was recorded to substantiate the presence of carbonyl group conjugated to the vinyl group. The new acrylates were added to basic formulation and exposed to UV radiation to get transparent films. The dynamic mechanical properties of the films cast from the formulations were assessed and studies on the effect of the synthesized crosslinking acrylate content and their nature on the viscoelastic properties of the films were carried out. Improvements in glass transition temperature (T_g) were observed with increasing percentage of crosslinker. Acrylates based on aromatic acid amides showed higher T_g than aliphatic acid amides. The storage modulus (E′) increased up to 10% and further increases in the crosslinker percentage led to a decrease in the modulus. The rubbery modulus depended on percentage of crosslinker and not on crosslinker structure.     

α- and γ-tocopherols as efficient antioxidants in butter oil triacylglycerols

Although tocopherols are known to be the most important natural antioxidants in fats and oils, controversial findings of their effects have been made in different model systems. The aim of the experiment was to study the effects of α- and γ-tocopherol at the levels of 2–500 μg/g on the oxidation of purified butter oil triacylglycerols (BO TAGs) at 40°C in the dark for 16 days. Both of the tocopherols were effective antioxidants. Although BO TAGs without additions began to oxidize immediately, BO TAGs with tocopherols remained in the induction period throughout the experiment. The antioxidant strength of α-tocopherol was less than that of γ-tocopherol. More hydroperoxides were formed in BO TAGs with at least 100 μg/g α-tocopherol than with less α-tocopherol at the same time being much less than in BO TAGs without tocopherols. Moreover, as the formation of secondary oxidation products in BO TAGs with tocopherols was negligible, no pro-oxidative effect of tocopherols could be found. At low concentration (≤ 10 μg/g) γ-tocopherol was slightly less stable than α-tocopherol.     

Novel high‐solids pigmented coatings prepared from a new‐synthesized isophthalate‐based oligoester,a melamine resin,and various fillers

A new‐synthesized hydroxyl‐terminated isophthalate‐based liquid oligoester (L‐311), an hexakis(methoxymethylol)melamine resin, and various inert pigments (fillers) such as either kaolins (Al₂O₃ · 2SiO₂ · 2H₂O) of different particle sizes (1.50 and 4.80 μm) or calcium metalsilicate (CaSiO₃) were used to prepare high‐solids pigmented coatings (PA and PW series, respectively). The physical, chemical, and mechanical properties (pencil hardness, Knoop hardness, flexibility, impact resistance, adhesion, gloss, solvent, and mar resistance) of the new‐formulated pigmented coatings were correlated to the chemical species of the filler, the filler's load and particle size, the quantity of the crosslinker, and the introduction of large particle size colloidal silica into the coating. For measuring the mar resistance of the pigmented coatings, the Taber abrasion method was applied and the inverse wear index, F [=I^?1, cycles/cg (wear index l, weight loss (cg) per number of cycles)], was directly related to the mar resistance. Either when kaolins or calcium metalsilicates were used as fillers, the Knoop hardness, the impact, and mar resistance of the films were affected from the filler's load, whereas the quantity of melamine resin (crosslinker) affected the knoop hardness, the gloss, and the mar resistance. The fillers' particle size and the introduction of large particle colloidal silica affected mainly the mar resistance and the gloss, respectively. The pencil hardness of the PW‐pigmented coatings series (F‐2H) was higher than that of the PA‐series (B‐HB). The chemical composition of the inert pigment proved to be a very important parameter in the preparation of pigmented coatings with specific properties that aim to meet modern and particular demands for various end‐up uses. All the new‐formulated high‐solids (nonvolatiles by weight ～ 70%) pigmented coatings (PA and PW series) presented excellent adhesion (5B), flexibility (> 32%), methyl ethyl ketone (MEK) resistance (>200 rubs), high pencil hardness, good knoop hardness, and very good impact resistance (from 100 up to 160 in.‐lb), independently of the species of the filler (kaolins or calcium metalsilicate). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 576–590, 2002; DOI 10.1002/app.10309     

Synthesis and characterization of UV-curable waterborne polyurethane–acrylate ionomers for coatings

A new kind of ultraviolet (UV)-curable waterborne polyurethane–acrylate (PUA) ionomer, prepared from toluene diisocyanate (TDI), polyethylene glycol (PEG), dimethylolpropionic acid (DMPA), triethylamine (TEA), and 2-hydroxyethyl methacrylate (HEMA), was synthesized by the modified prepolymer mixing process in which water serves as a chain-extender and dispersant. Fourier transform infrared (FTIR) spectra demonstrated the formation of the PUA ionomers both in dispersions and in their corresponding cured films. Surface tension of the PUA dispersions decreased as the DMPA-to-PEG mole ratio increased. The investigation of rheological behavior of the PUA dispersions suggested that all the dispersions belong to pseudoplastic fluid and display the characteristic of common polymer dispersions. Differential scanning calorimetry (DSC) analysis showed that the increasing DMPA-to-PEG mole ratio may result in a higher T_g and a broader transition zone for the hard segment. The results of TGA for the PUA-cured films indicated good thermal stability with no appreciable weight loss until well above 200°C. Measurement of physical properties showed that all the PUA-cured films exhibited excellent adhesion, gloss, flexibility, and impact strength, as well as pendulum hardness, depending upon hard segment content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2869–2876, 1999     

Selective Debromination and α‐Hydroxylation of α‐Bromo Ketones Using Hantzsch Esters as Photoreductants

Two transformations initiated by photoinduced one‐electron transfer to α‐bromo ketones have been demonstrated. Hantzsch esters donate one electron to α‐bromo ketones under photoirradiation, promoting reductive debromination. Subsequent reactions of the resulting radical species of the ketones with molecular oxygen and Hantzsch esters lead to α‐hydroxylation or debromination, respectively. The relative dominance of the two pathways depends profoundly on the reaction conditions, including solvent, O₂ levels, and the concentration of the Hantzsch esters. The synthetic protocols feature advantages because they require the environmentally benign sources, molecular oxygen and visible light.

     

Photoinitiating behavior of bifunctional photoinitiator containing α‐hydroxyalkylphenone group on free‐radical polymerization

Photoinitiating behaviors of bis[4‐(2‐hydroxy‐isopropionyl)]ether photoinitiator on free‐radical polymerization have been investigated. The kinetics of photopolymerization initiated by the photoinitiator was studied by means of differential photocalorimetry. The bifunctional photoinitiator showed comparative performance with those commercial photoinitiators with monofunctional chromophoric group. The effect of UV intensity on the polymerization rate was investigated, and the value of exponential factor was found to be 0.5 at the beginning of polymerization, suggesting that the photopolymerization initiated by bis[4‐(2‐hydroxy‐isopropionyl)]ether followed biradical termination mechanism. Photosensitizer triethylamine improves the initiating efficiency while oxygen is shown to restrict polymerization in this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5297–5302, 2006     

Catalytic Hydrogenation of α‐Iminophosphonates as a Method for the Synthesis of Racemic and Optically Active α‐Aminophosphonates

It was shown that the catalytic hydrogenation of α‐iminophosphonates by molecular hydrogen can serve as a convenient method for the synthesis of racemic and optically active α‐aminophosphonates. Up to 94% ee was achieved in the rhodium‐catalyzed enantioselective hydrogenation using chiral ligand (R)‐BINAP.     

Synthesis of α‐Arylphosphonates using Copper‐Catalyzed α‐Arylation and Deacylative α‐Arylation of β‐Ketophosphonates

Efficient methods for the direct arylation and deacylative arylation of β‐ketophosphonates with iodoarenes in presence of a copper(I) or a copper(II) salt as the catalysts have been developed. The corresponding α‐arylphosphonates were obtained in high yields. A tentative mechanism for the deacylative arylation reaction was proposed on the basis of the experimental data.     

Influence of isomer ratio and ring substituents in decomposition activation energies of α,α,α′,α′‐tetrasubstituted dibenzyls

Diethyl‐2,3‐dicyano‐2,3‐di‐(X‐substituted phenyl) succinates (X = p‐OCH₃, p‐CH₃, p‐Cl, H, p‐NO₂) can initiate the free‐radical polymerization of styrene. The decomposition rate constant and activation energy were measured by means of a dilatometer, and the results showed that they were strongly dependent on the ratio of meso‐ and dl‐isomers in the polysubstituted dibenzyl compounds and the properties of the ring substituents. On the other hand, it was found that the polystyrenes, which were obtained by initiation with hydrogen, had a much larger average molecular weight than that with p‐OCH₃ and p‐CH₃. The experimental phenomena were correlated with the structure of the radical resulting from hydrogen. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2964–2971, 2001     

α‐, γ‐ and δ‐ Tocopherols as inhibitors of isomerization and decomposition of cis,trans methyl linoleate hydroperoxides

The effects of α‐, γ‐ and δ‐tocopherols on the stability and decomposition reactions of lipid hydroperoxides were studied. Isomerization and decomposition of cis,trans methyl linoleate hydroperoxides (cis,trans ML‐OOH) in hexadecane at 40 °C were followed by high‐performance liquid chromatography. Due to its higher hydrogen donating ability, α‐tocopherol was more efficient than γ‐ and δ‐tocopherols in inhibiting the isomerization of cis,trans ML‐OOH to trans,trans ML‐OOH. α‐Tocopherol stabilized hydroperoxides into the cis,trans configuration, whereas γ‐ and δ‐tocopherols allowed hydroperoxides to convert into trans,trans isomers. Thus, the biological importance of α‐tocopherol as compared to other tocopherols may be partly due to its better efficacy in protecting the cis,trans configuration of hydroperoxides formed, for example, in the enzymatic oxidation of polyunsaturated fatty acids. The isomeric configuration of hydroperoxides has an impact on biological activities of further oxidation products of polyunsaturated fatty acids. Paradoxically, the order of activity of tocopherols with regard to hydroperoxide decomposition was different from that obtained for hydroperoxide isomerization. γ‐ and δ‐tocopherols were more efficient inhibitors of ML‐OOH decomposition when compared to α‐tocopherol. A loss of antioxidant efficiency, observed as the tocopherol concentration increased from 2 to 20 mM, was highest for α‐tocopherol but was also evident for γ‐ and δ‐tocopherols. Thus, the differences in the relative effects of tocopherols at differing concentrations seem to result from a compromise between their radical scavenging efficiency and participation in side reactions of peroxidizing nature.     

Enantioselective Phase‐Transfer Catalytic α‐Benzylation and α‐Allylation of α‐tert‐Butoxycarbonyllactones

A new enantioselective α‐benzylation and α‐allylation of α‐tert‐butoxycarbonyllactones was devloped. α‐Benzylation and α‐allylation of α‐tert‐butoxycarbonylbutyrolactone and α‐tert‐butoxycarbonylvalerolactone under phase‐transfer catalytic conditions (50% cesium hydroxide, toluene, −60 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐NAS bromide (1 mol%) afforded the corresponding α‐substituted α‐tert‐butoxycarbonyllactones in very high chemical yields (up to 99%) and optical yields (up to 99% ee). The synthetic potential of this method has been successfully demonstrated by the asymmetric synthesis of unnatural α‐quaternary homoserines, 3‐alkyl‐3‐carboxypyrrolidine and 3‐alkyl‐3‐carboxypiperidine.     

Soybean oil based resin: A new tool for improved immobilization of α‐amylase

Acrylated epoxidized soybean resin has been utilized to immobilize the α‐amylase via UV‐curing technique. Among the numerous methods that exist for enzyme immobilization, entrapment and covalent binding are the focus of this study. The properties of immobilized enzyme were investigated and compared with those of the free enzyme. Upon immobilization by the two methods, the catalytic properties of the enzyme were not considerably changed as compared with that of nonimmobilized form; only the pH profile was broadened for the immobilized enzyme. The free enzyme lost its activity completely in 20 days, where as storage and repeated usage capability experiments demonstrated higher stability for the immobilized form. Immobilized enzyme prepared by attachment method possesses relatively higher activity compared with the activity of those obtained by entrapment method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4757–4761, 2006